What type of electrical current consists of sine waves of constant amplitude but different frequencies from two sources?

Interferential Current is the correct answer because it is a therapeutic method used in electrotherapy that employs two mediums of alternating current at different frequencies. When these two currents intersect, they create a resultant current that varies in amplitude due to the interference of the two sine waves. This technique can promote pain relief and muscle stimulation more effectively than a single frequency alone.

In contrast, direct current (DC) flows steadily in one direction and does not consist of sine waves or varying frequencies. Alternating current (AC) involves voltage that alternates over time but does not necessarily have the same interference effect created with two different frequency sources. Pulsed current refers to a kind of electrical current that is delivered in intermittent bursts, which is distinct from the continuous wave nature of interferential current. Therefore, it is the unique interaction of two sine waves of different frequencies that defines interferential current as the correct choice.